This invention relates to radiation sensitive devices for instantly monitoring a high dose of high-energy radiations, such as electrons, X-rays, protons, alpha particles and neutrons using color-changing materials. More particularly, the present invention is related to a radiation dosimeter which provides instant exposure results and which can be easily adhered to a second radiation detector and dosimeter.
We are exposed to a wide variety of toxic chemicals and biological agents—through our air, water and food—that are hazardous to our health and can potentially induce cancer. At low levels of exposure, these agents either cause little harm to us or the harm is within the acceptable risks. Hence, they are not monitored. However, when the exposure level is expected to be high, e.g., at work places, toxic chemicals and biological agents are monitored.
There are selective detectors/monitors for monitoring exposure to some individual hazardous chemicals and biological agents. As we are exposed to many hazardous chemicals and biological agents, it is not possible to monitor all of them individually or jointly. However, it is possible to monitor radiation selectively. Typically, we monitor exposure to radiation at levels way below the acceptable risks. There is a need for a dosimeter which instantly monitors hazardous dose of ionizing radiation so preventive measures can be taken. Color changing/developing instant radiation dosimeters for monitoring low dose, e.g., 0.1 to 1,000 rads, have been reported recently in commonly assigned U.S. Pat. No. 5,420,000; PCT publication number WO2004/017095 and PCT Application No. PCT/US2004005860 each of which is incorporated herein by reference thereto.
If a person is exposed to radiation, especially a high dose (e.g., 50 rads), there are predictable changes in the body that can be measured. The number of blood cells and the frequency of chromosome aberrations in the blood cells are examples of biomarkers used to indicate radiation exposure. Rapidly dividing cells are more susceptible to radiation damage. Examples of radiosensitive cells are blood forming cells (bone marrow), intestinal lining, hair follicles and fetuses. Hence, these develop cancer more readily. The risk for radiation exposure has been very widely studied.
It is well established that a high dose of ionizing radiation can cause cancer and other problems. At 0 to 25 rads there is no easily detectable clinical effect in humans. However, at about 15 rads there could be temporary sterility particularly in the case of testicular radiation. At about 25 to 100 rads a slight short-term reduction in blood cells is observed but disabling sickness is not common. At 100 to 200 rads nausea and fatigue is observed, vomiting occurs at doses greater than 125 rads and longer-term a reduction in the number of some types of blood cells is observed. At 200 to 300 rads nausea and vomiting typically occur on the first day of exposure. There may be up to a two-week latent period followed by appetite loss, general malaise, sore throat, pallor, diarrhea, and moderate emaciation. Recovery usually occurs in about three months unless complicated by infection or injury. At 300 to 600 rads nausea, vomiting, and diarrhea occur in the first few hours. There may be up to a one-week latent period followed by a loss of appetite, fever, and general malaise in the second week followed by bleeding, inflammation of mouth and throat, diarrhea, and emaciation. Some deaths occur in two to six weeks. Eventual death of 50% of victims is expected if exposure is above 450 rems. Recovery time is about six months. Over 600 rads nausea, vomiting, and diarrhea occurs in the first few hours followed by rapid emaciation and death in the 2nd week. Eventual death of nearly 100% of victims is expected.
There is no doubt that radiation can cause cancer. The question is what level of radiation it takes to cause cancer. Some believe that this low level is about 20 rads. Below this dose it is not possible to detect adverse health effects. The Health Physics Society has issued a position statement indicating that there are no observable health effects below 10 rems but that health risks, if they exist below 10 rems, are too small to be observed. (Note: 1 rem is almost equivalent to 1 rad for tissue equivalent materials). No one knows whether there is any risk or not. All we can say now is that no one has detected any statistically significant effect at doses below about 100 mSv (10 rems). Some epidemiological studies suggest an increased risk of cancer in the 15-20 rads dose range. However, the data suggest that risks in the 15-20 rem dose range are very small and difficult to measure. Above 10 rems there appears to be a significant risk of thyroid cancer due to radioiodine exposure in children 15 years of age and younger. The general consensus of opinion for the radiation induction of cancer is a 10% increase in cancer rate/100 rem when the dose is given over a short time with a decrease to 5% when the dose is protracted over an extended time period. This raises an interesting question; what dose range is more important to monitor, 10 mrem-25 rems, 1-1,000 rems, or 10 mrem-1,000 rems?
A large number of radiation detectors, monitors and dosimeters are used for detecting and monitoring radiation. The most popular being ionization chambers, proportional counters, Geiger-Mueller counters, scintillation detectors, semiconductor diode detectors, and dosimeters such as TLD, X-ray film and track etch. Track etch type dosimeters are usually used for monitoring high LET (linear energy transfer) particles, such as alpha particles.
Ionizing radiations, such as X-ray and neutrons, need to be monitored because they have high penetration power and can cause cancer. TLDs (Thermoluminescence dosimeters) and X-ray film dosimeters are widely used for monitoring personal exposure to X-ray radiation. TLD and X-ray film can monitor radiation over a very wide dose range, e.g., 10 mrem −1,000 rems. However, they are not instant and self-reading. They need to be sent to a laboratory for determination of the dose, which may take several days. Electroscope ionization chamber dosimeters, often called quartz or carbon fiber dosimeters, are instant and self-reading but they are the most fragile dosimeters. There are small electronic dosimeters but they are expensive, need batteries and are not resistant to severe conditions, such as very high or low temperatures and water (e.g., laundry cycle). Radiation counters, such as proportional and Geiger-Mueller counters, are not dosimeters. In an event of nuclear detonation, these counters will be overwhelmed and may not monitor total dose exposure.
Tens of millions of radiation dosimeters, such as TLD and X-ray film, are used for monitoring low dose every year. The monitoring period for these dosimeters is typically one to three months. If a person is exposed to high dose, e.g., between 1 and 25 rads, it would take days to months before it is known. Additionally, what we need to monitor are two major exposures (1) high dose instantly and (2) legally allowed dose, e.g., 5 rads/year for nuclear/radiation workers or 25 rads for a lifetime. It is required that we monitor harmful high dose instantly and total dose per year and/or lifetime.
There is also a need for an area dosimeter for areas around radioactive materials, radiation sources, nuclear power plants, nuclear submarine and shipment of radioactive material to monitor radiation dose instantly. A sticker type self-indicating instant radiation dosimeter would be very convenient to use as an area dosimeter.
Hence, there is an ongoing and critical need for a dosimeter, either individually or attached to other dosimeters and detectors, especially when the threat of radiological terrorism is high, which is (1) instant, (2) simple and self-indicating, (3) lightweight so it may be carried on a person at all times or applied to other dosimeters and detectors, (4) inexpensive and disposable, (5) practically non-destructible, (6) can withstand severe ambient and environmental conditions, such as laundry cycle, (7) tamperproof or tamper evident, (8) does not need any external power, such as a battery, (9) integrates the dose for at least one year, (10) tissue equivalent so that no dose correction is required, (11) retains the dose value and the results/dose can be archived, (12) monitors wide dose range (0.1-1,000 rads), (13) monitors all kinds of harmful radiations, such as X-ray, neutrons and high energy electrons over a very wide temperature range (e.g., −20° C. to 60° C.) and (14) independent of energy and dose rate. The dosimeters described in U.S. patent application Ser. No. 10/545,796 filed Sep. 6, 2005 and that described herein meet these requirements.